The present invention relates generally to a manner by which to facilitate communication of data upon a communication channel susceptible to fading, such as a communication channel used during operation of a cellular, or other, radio communication system. More particularly, the present invention relates to apparatus, and an associated method, by which to encode data to form a concatenation of systematic, recursive, space-time codes that complies with an equal eigenvalue criterion. Concatenation of the codes is performable, and the codewords from the concatenated encoder are applied to a multiple-antenna set to be transduced into electromagnetic form for communication upon the communication channel.
Communication of data between remotely-positioned sending and receiving stations is a necessary adjunct of modern society. A wide variety of different types of communication systems have been developed and are regularly utilized to effectuate communication of data between the sending and receiving stations.
Advancements in communication technologies have permitted the development, and commercial implementation, of new types of communication systems. Radio communication systems are exemplary of communication systems which have benefitted from the advancements in communication technologies. Improvements to existing types of radio communication systems as well as new types of radio communication systems have been made possible as a result of the advancements in communication technologies.
Use of a radio communication system inherently permits increased communication mobility in contrast to use of a conventional wire line communication system. Communication channels defined between sending and receiving stations of a radio communication system are defined upon radio links formed therebetween. The communication channels are referred to as radio channels and do not require fixed connections for their formation.
The advancements in communication technologies include, for instance, the use of digital communication techniques. The use of digital communication techniques permits the communication capacity of a communication system to be increased as well as also to improve the quality levels of communications effectuated in the communication system.
Information which is to be communicated in a digital communication system is digitized. Once digitized, the digitized information is formatted, such as into data packets, and converted into a form to permit its communication upon the communication channel. In an ideal communication system, the data packets, subsequent to transmission upon the communication channel and reception at a receiving station, are substantially identical in value to the corresponding data packets prior to their communication upon the communication channel. In an actual communication system, however, distortion is introduced upon the data during its communication upon the communication channel such that the values of the data, when received at the receiving station, differ, in part, from corresponding values of the data packets prior to its communication upon the communication channel. If the amount of distortion is significant, the informational content of the data cannot accurately be recovered at the receiving station.
Multipath transmission, for instance, causes fading of the data. Such fading might alter the values of the symbols of a data packet during its transmission upon the communication channel. Quasi static flat fading, for example, models a situation in which fading is flat in frequency and is constant during duration of a relevant block of transmitted signals. In contrast, fast flat fading models a situation in which fading is flat in frequency but changes as fast as from a block of (transmitted) complex symbol epochs to a subsequent block of complex symbol epochs; here a block consists of at least one epoch. If the propagation distortion is not properly corrected, resultant communication quality levels of the communications are, at a minimum, reduced.
Various techniques are utilized to compensate for the distortion introduced upon the data as a result of communication of the data upon a non-ideal communication channel. Increasing the diversity of the data is utilized, for instance, to increase the likelihood that the informational content of the data can be recovered.
Encoding of the data, prior to its communication, by creating redundancy in time can be viewed as time diversity. When the data is encoded, the redundancy of the data is increased. Because of the increased redundancy, loss of portions of the data due to fading is less likely to prevent the recovery of the informational content of the data.
Space diversity at the transmitter end is also utilized to compensate for distortion. Typically, transmit space diversity refers to the utilization of more than one transmit antenna at a sending station at which to transduce the data. The antenna transducers are separated by distances great enough to ensure that the data communicated from the respective transducers fade in an uncorrelated manner. Fading of the data transmitted upon one communication path to a receiving station is thereby less likely to fade in the same manner and at the same time as data communicated to a receiving station upon a different communication path.
Space and time diversity are sometimes utilized together, thereby further to enhance transmission diversity to combat signal fading caused, e.g., by multi path transmission.
Various coding techniques have been developed for use in transmit diversity schemes. Space-time codes have been developed to achieve diversity when transmitted upon fading channels by implementing redundancy at a sending station in both space and time. Traditional systematic and recursive codes are known. Systematic and recursive codes are advantageous in concatenating at least two codes, to form so-called xe2x80x98turboxe2x80x99 codes, which are to be decoded iteratively. However, systematic and recursive, space-time codes have generally not been available. Additionally, an equal eigenvalue condition can be imparted on at least those pairs of codewords separated by the smallest symbol Hamming distance, in order to benefit a concatenation of codes. This feature, along with the apparatus and associated method, constitutes the object of this invention.
It is in light of this background information related to communication of data upon a channel susceptible to fading that the significant improvements of the present invention have evolved.
The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to facilitate communication of data upon a communication channel susceptible to fading, such as a radio communication channel used during operation of a cellular, or other, communication system.
Through operation of an embodiment of the present invention, data is encoded to form codewords that are generated, e.g., via parallel-concatenated space-time encoders, possibly with puncturing. The constituent encoders pertain to systematic, recursive, space-time codes. And, the codewords resulting from the concatenated encoders are applied to a multiple antenna set to be transduced therefrom.
In one aspect of the present invention, apparatus is provided for a sending station, operable to send a communication signal representative of data that is to be communicated to a receiving station. At the sending station, the data that is to be communicated is encoded by individual, constituent space-time encoders, which are chosen to form a concatenation scheme and perform, e.g., trellis encoding of the data according to the constituent space-time codes representative of some choice of coded representations of data, which form the concatenation. A constituent encoder""s implementation includes a feedback path, and the encoder is constructed such that the codeword formed thereat is both systematic and recursive. The codeword has characteristics to facilitate communication upon communication channels having multiple propagation paths that result in fading.
In another aspect of the present invention, separate constituent space-time encoders are coupled to receive indications of the same data. That is to say, data that is applied to a first space-time encoder is also applied to a second space-time encoder. The data applied to the second space-time encoder is interleaved prior to application thereto. Each of the space-time encoders encodes the data applied thereto to form codewords at the outputs of the respective encoders. The codewords formed by the respective encoders are concatenated together in a meaningful way, e.g., in parallel to form parallel-concatenated codewords, perhaps with puncturing of some parts of their respective outputs. The parallel-concatenated codewords are applied to an antenna transducer set to be transduced therefrom. Space-time diversity provided to the data to be communicated by a sending station to a receiving station facilitates communication of the data to a receiving station in a form that permits the informational content of the data, once received at the receiving station, to be recreated. Because the space-time codes formed by the respective constituent space-time encoders are both systematic and recursive, the concatenation of the respective codes formed via the respective space-time encoders is lucrative.
In one implementation, a systematic, recursive, eight-state, constituent space-time encoder is used. In another implementation, a systematic, recursive, sixteen-state, space-time encoder is used. The space-time encoder is implemented, for instance, at a base transceiver station of a cellular, or other radio, communication system. When data to be communicated, such as data packets formed pursuant to effectuation of a packet-based communication service, recovery of the informational content of the data packets at a mobile station that receives the data packet is facilitated.
In these and other aspects, therefore, apparatus, and an associated method, is provided for a sending station operable in a communication system to send data upon a communication channel susceptible to fading. Channel-encoded data is formed. A first encoder is coupled to receive first values representative of the data to be communicated upon the communication channel. The first encoder translates the first values representative of the data into first encoded form. The first encoded form is used to construct a first codeword. The first codeword is of a systematic, recursive space-time code that complies with an equal eigenvalue criterion. A second encoder is coupled to receive second values representative of the data to be communicated upon the communication channel. The second encoder translates the second values into second encoded form. The second encoded form is used to construct a second codeword of a systematic, recursive space-time code that also complies with equal eigenvalue criterion. At least selected parts of both the first and second codewords form the channel-encoded data, so as to verify an equal eigenvalue condition for at least those pairs of codewords separated by the smallest symbol Hamming distance.